A self-transmissible, low-copy plasmid used for the generation of single-stranded DNA when infected with M13 phage; may contain a resistance marker to allow maintenance and will often carry the lacI and lacZ∆M15 genotypes

galK

Galactokinase mutation blocks catabolism of galactose—cells that are galK minus grow in the presence of galactose as the sole carbon source

galU

Glucose-1-phosphate uridylyltransferase mutation blocks ability to use galactose—cells that are galU minus can grow on media that contains galactose as the sole carbon source

gyrA96

DNA gyrase mutant produces resistance to nalidixic acid

hsd

Mutations in the system of methylation and restriction that allow E. coli to recognize DNA as foreign. The hsd genotype allows efficient transformation of DNA generated from PCR reactions *hsdR–eliminates restriction of unmethylated EcoK I sites. (1) **hs

lacI

Encodes the lac repressor that controls expression from promoters that carry the lac operator; IPTG binds the lac repressor and derepresses the promoter; often used when performing blue/white screening or to control expression of recombinant genes

lon Deficiency in the Lon ATPase-dependent protease; decreases the degradation of recombinant proteins; all B strains carry this mutation

mcrA, mcrBC,or mrr

Mutations that allow methylated DNA to not be recognized as foreign; this genotype is necessary when cloning genomic DNA or methylated cDNA

nupG

Mutation for the transport of nucleosides

ompT

Indicates that the E. coli lack an outer membrane protease—reduces degradation of heterologous the strains and recovery of intact recombinant proteins is improved in ompT minus strains

P3

A 60-kb low-copy plasmid that carries the ampicillin and tetracycline resistance genes with amber mutations; used predominantly for selection of supF-containing plasmids; carries the kanamycin resistance gene for selection

Mutation in a gene responsible for general recombination of DNA; particularly desirable when cloning genes with direct repeats

relA

RNA is synthesized in absence of protein synthesis (relaxed phenotype) relA locus regulates the coupling between transcription and translation. In the wild type, limiting amino acid concentrations results in the shutdown of RNA synthesis (also known as th

rpsL

Confers resistance to streptomycin (this makes a mutant ribosomal protein, small subunit, the target of the drug)